Voltage divider



Sept. 13, 1955 w J, RE S 2,717,942

VOLTAGE DIVIDER Filed June 16, 1952 4 Sheets-Sheet l FIG. 2.

W/LL/AM J. ANDREWS BY M @flw P 13, 1955 w. .1. ANDREWS 2,717,942

VOLTAGE DIVIDER Filed June 16, 1952 4 Sheets-Sheet 2 Eli E 120 E 240 EA:E I20 E 240' s[o PICK- OFF, E A:

/ R'= FILAMENT TO FILAMENT RESISTANCE E 4 PHASE TO PHASE RESISTANCE I E:20 R= APPROXIMATELY E 4240' WHE $E 7Z=TOTAL NUMBER OF FILAMENTSPICK-OFF EA FIG. 4.

INVENTOR. WILL/AM J. ANDREWS BY 6 /7M Sept. 13, 1955 w. J. ANDREWSVOLTAGE DIVIDER 4 Sheets-Sheet 3 Filed June 16, 1952 p MECHANICAL ANGLEuwdtm EDEFOMJM Sept. 13, 1955 2,717,942

W. J. ANDREWS VOLTAGE DIVIDER Filed June 16, 1952 4 Sheets-Sheet 4 CLO "FIG O I I I I I 4| 0 I l I I I I J 0 00 120 |a0 240 300 360 420 0 60 |ao240 300 360 420 ELECTRICAL PHASE 0 "I ELECTRICAL PHASE 0 I l I 4 -60 5040 20 I0 0' [0 20 30 [3, MECHANICAL DEGREES INVENTOR.

WILLIAM J. ANDREWS I I J {5, MECHANICAL DEGREES United States PatentVOLTAGE DIVIDER William J. Andrews, Lancaster, Pa., assignor to theUnited States of America as represented by the Secretary of the NavyApplication June 16, 1952, Serial No. 293,719

Claims. (Cl. 20155) The present invention relates to continuouslyadjustable voltage dividers, and, more particularly, to voltage dividersdeveloped for use with polyphase alternating current systems, wherebysmooth transitions between the instantaneous voltages of the respectiveconductors may be attained.

Heretofore there has been no satisfactory simple apparatus foraccomplishing this result, for ordinarily a usable device for thispurpose would require a large number of series-connected resistors ofthe voltage divider type to give the required continuous variationthrough the multiple phases over and over again in proper order ofsuccession.

A principal object of this invention, therefore, is to provide a simpleand reliable polyphase voltage divider.

Another object is to provide a polyphase voltage divider that can bemade very compact without losing its smoothness of voltage control.

To provide a polyphase voltage control whereby various rates ofvariation may be secured by radially shifting the location of a contactelement that slidingly contacts the resistor of the voltage divider, isanother main object of this invention.

A still further object of the invention is to provide a polyphasevoltage divider having a plurality of independent voltage dividersections, each having an individual contact element that is likewiseadjustable independently of any other contact element.

Other objects and many of the attendant advantages of this inventionwill be appreciated readily as the same becomes understood by referenceto the following detailed description, when considered in connectionwith the accompanying drawings, wherein:

Fig. 1 is a face view of the multiple resistor of an adjustable voltagedivider, embodying the invention;

Fig. 2 is a cross-section taken along line 22 of Fig. 1;

Fig. 3 illustrates a multi-tap resistance potentiometer equivalent tothe arrangement shown in Fig. 1;

Fig. 4illustrates the potentiometer of Fig, 3 connected in a three-wiredelta arrangement;

Fig. 5 illustrates a vector diagram for the arrangements shown in Figs.3 and 4;

Fig. 6 illustrates graphical representations of theoretical phase errorangle versus mechanical motion in equivalent electrical degrees of thepick-off for three and four phase excitations;

Fig. 7 illustrates the graphical representation of electrical phaseangle versus mechanical angle for a typical segment of section 12 of thepotentiometer arrangement shown in Fig. 1;

Fig. 8 shows the graphical representation of theoretical output voltageversus electrical phase angle for an arbitrary selected value of maximumpick-off voltage measured with respect to ground of two (2) volts;

Fig. 9 shows a graphical representation of output voltage versuselectrical phase angle for a typical segment of section 12 of thepotentiometer arrangement illustrated in Fig. 1;

Fig. 10 illustrates a graphical representation of output voltage versuselectrical phase angle for another typical segment of section 12 of thepotentiometer arrangement in Fig. 1;

Fig. 11 illustrates a graphical representation of lobe pattern as afunction of mechanical motion of section 12 of the potentiometerarrangement of Fig. 1; and

Fig. 12 illustrates a graphical representation of a lobe pattern as afunction of mechanical motion for section 16 of the potentiometerarrangement of Fig. l.

The device is designed to be used with a star-connected polyphase powersystem, having a neutral return conductor. The voltage divider has acharacteristic repetition pattern of conducting lines, each interval ofwhich has the same number of lines as the number of phases of the powersystem. Thus in the present case, designed for use with a three-phasepower source, there are three lines in each interval. Consequently thefourth, fifth and sixth lines are electrically connected with the first,second and third line, respectively, and so on, the third line followingany given line thus representing the same conductor of the three-phasepower supply mains.

As the voltage divider is to be used in apparatus wherein space isextremely limited, it must be made as small as is consistent withadequate performance, and hence the lines must be spaced closely, whichin turn requires that the width of each line should be as small as isreadily feasible, and that the lines he placed as nearly uniformly aspossible. For example, in one type of voltage divider wherein theconductors are carried by a Bakelite disk having a diameter of threeinches, the lines do not exceed 0.002" in width and are positionedwithin a maximum tolerance of 0.0005".

The conducting lines mentioned above are preferably metallic andadvantageously may consist of silver. They may be applied to the surfaceof the Bakelite disk in any suitable way, for example, by printing, ofthe kind used in printed radio circuits. The lines, however, form merelythe underlying network which is covered by a uniform coating ofresistance material. This is preferably of a relatively high-resistancetype, having a value exceeding 50,000 ohms per square. Such high valueis chosen because of the close spacing of the conductive lines, whichotherwise would produce undesirably low resistances between consecutivelines.

Referring now to Fig. 1 for a detailed description of the invention,there is shown a circular disk 10 made of insulating material havingsuitable mechanical characteristics. It has been found, for example,that Bakelite and certain other synthetic resins are satisfactory forthe purpose. In section 12 of the disk 10 there are several sets ofparallel conducting lines, while sections 14 and 16 have sets ofconvergent conducting lines.

In section 12, the first conducting line 18 at the left is connectedthrough a heavier conductor 20 to a projection 22 of an innermost busbar 24 which is shown as circular with projections 22 and 26 extendingtherefrom to facilitate making connections thereto. Counting to theright and in the clockwise direction in section 12, the fourthconducting line 27 is, likewise, electrically connected to projection 22through the conductor 28, and so on progressively, with the result thatevery third line after conducting line 27 of the parallel series isconnected to the bus bar 24. An enlargement of bus bar 24, shown at 29,connects through to the other face 30 of the disk 10 to a preferablysilver slip ring 31 which will be described presently. The connection ismade through a hole 32 filled with silver paste.

The second of the parallel conducting lines of section 12 is designatedas 33 and it is connected electrically through a heavier conductor 34 tothe outermost bus bar 36 which is, likewise, of general circular shape,and has a tab 37 extending inwardly for connection to a second silverslip ring 38 on the other face of disk 10. This connection to slip ring38 is made through a silver paste filled post 39. The line 33, like line18, is also the first member of a series of parallel lines, comprisingthis line 33 and every third line to the right therefrom so thatbeginning with line 33 every third line therefrom is connectedelectrically to the bus bar 36.

Finally, the third conducting line 40 at the left of section 12 isconnected by a heavier conductor 42 toa third bus bar 44 which includesa series of projections 46 between the successive conductors of theseries 34 that connects to bus bar 36. The projections or lugs 46 areinsulated from bus bar 36, but are all individually connected to a thirdslip ring 48 on face 30 by silver paste filled posts in the form of apin, such as indicated by 50. As in the other series, starting with line40 every third line therefrom and counting to the right, is connected tothe adjacent lug 46, and these lugs 46, in turn, are all connected to athird silver slip ring 48 on the other face 30 of the disk 10.

It will be seen that section 12 has now been described as comprising aseries of parallel conductors, connected in regular order to the threebus bars 24, 36, and 44.

The first conducting line 54 in the converging series of conductinglines in section 14 at the left is connected through a heavier conductor56 to the outermost bus bar 36. Counting to the right, that is in thecounterclockwise direction, in section 14, the fourth conducting line58, likewise, is electrically connected to bus bar 36 through a heavierconductor of the type indicated by 56, and so on progressively, with theresult that every third conducting line to the right from line 58 of theconverging series is connected to the bus bar 36.

The second conducting line 60 of the converging series of lines ofsection 14 is electrically connected through a heavier conductor 62 tobus bar 24. Beginning with line 60, every third line thereafter, movingto the right, is connected through a heavier conductor to bus bar 24.

In section 14, the third conducting line 64 of the series of converginglines, and every third line thereafter, is electrically connected to thethird bus bar 44 through lugs or projections 65 and heavy conductors,such as 66.

All three sets of conducting lines, as previously indicated for theconducting series in section 12, are connected to their respective sliprings 38, 31, and 48 on face 30 of the circular disk 10.

The conducting lines 67, 68, and in section 16 are connected in the samemanner as the lines 54, 60 and 64, in section 14. Each third linethereafter from lines 67, 68, and 7t) (counting to the right) isconnected like in section 14. It is to be pointed out that the number ofcontacts and lines in section 16 does not necessarily have to be of thesame number as the contacts and lines in section 14.

It is to be noted further that the lines of section 14, such as 54, 60,and 64, as well as the lines 67, 68, and 70, do not converge at thecenter 72 of the circular disk 10, but at different off-center points,such as indicated by 74 and 76. As will be presently pointed out, thisis done so that a contactor located a greater radial distance from thecenter 72 of the circular disk 10, will contact a smaller number oflines, such as 54, 60, and 64, than a contactor located at a shorterradial distance from the center 72 of the circular disk 10, for the sameangular movement of the contactors.

In each section, namely sections 12, 14, and 16, a suitable resistancematerial, such as carbon in graphite form, is deposited or printed inuniform thickness on the surfaces 78, 80, and 82 of disk 10 so as toembed all the conducting lines, such as 18, 33, 40, and 27 in section12, lines 54, 60, and 64 in section 14, and lines 67, 68, and 70 insection 16, and so forth in each section, and

also to offer the necessary resistance between the sets of conductinglines.

There is one major difference between the arrangement of the conductinglines in section 14, and the conducting lines of section 16. In sections14 and 16, it is to be observed that the angular spacings betweenconducting lines, such as 54 and 60, or 60 and 64, and so on, in section14, are greater than the angular spacings between conducting lines, forexample, 67 and 68 or 68 and 70, and so on, in section 16. Theconducting lines of these sections 14 and 16 have been arranged in thismanner so as to give a difference in the proportionality constant (thatis a variable gyro compensation factor of angular rate to phase). Thus,with the wider angular spacings in section 14, a smaller phase change isobtained with a fixed angular rate than is obtained for section 16 whichcontains the closer angular spacings of conducting lines.

Scales 84, 86, and 88, corresponding to various values of a gyrocompensation factor, are provided as indicated.

In section 12, the parallel conducting lines have been arranged so thatthe gyro compensation factor (or proportionality constant) varies as thecosine of the angle measured between a vertical line passing through thecenter of the section 12 and the center 72 of circular disk 10, and theinstantaneous position or location of a contactor or pointer, that is, aline passing through the location of the contactor and the center 72 ofcircular disk 10.

In the converging sections 14 and 16, the change in phase angle islinear with the change in angle. Thus, for example, in section 14, thephase angle at conducting line 54 would correspond to 0 phase angle, atconducting line 60 to 120 phase angle, at conducting line 64 to 240phase angle, and at conducting line 58 to 360 or 0 phase angle, and willthus repeat thereafter as previously indicated. Thus between conductinglines 54 and 60, the phase angle changes 120. Half way between these twoconducting lines 54 and 60, the phase angle would be 60. By means ofthis arrangement in sections 14 and 16, the phase that the signal isdeviated from the reference signal will, therefore, be directlyproportional to the rate of change of angular position.

The multi-tap, phase shifting potentiometer thus described can beutilized for possible use as the free gyro take-off element in the phasefollow-up scanning interferometer system. It is one of the properties ofsuch a take-off element that a small angular motion of the gyro willproduce a 360 phase shift in output signal. Another property is that theangular rnotion-output phase relationship will be a continuous andessentially linear function over discrete regions of the potentiometer.Another important advantage of the system described so far is thatcertain non-linear compensation factors can be introduced over arelatively broad region of the potentiometer.

Briefly reviewing the potentiometer described in detail above, itcomprises a gridwork of fine silver filaments, such as 18, 33, and 40,and the like applied to a Bakelite disk 10 and overlaid with a thincoating of resistance material, such as graphite. The pick-off for thepotentiometer is merely a contact button which slides over theresistance material, and is constrained radially at a pointcorresponding to the center 72 of disk 10.

The various filaments or conducting lines, such as 18, 33 and 40, areenergized by a three phase A. C. source so that, as previously pointedout, adjacent conducting lines carry voltages which differ in phase by120", that is, in sequence: 0, 120, 240, 0, 120, and 240.

With the resistance material overlay, such as deposited in the areas 78,80, and 82, on the conducting lines or filaments, this assembly becomesequivalent to a multitap, resistance potentiometer as shown in Fig. 3.It is at once apparent that each set of four (4) filaments or conductinglines 94, 96, 98, and constitutes a delta connected resistance load.Since the conducting lines 94 and 100 are energized by identical phasevoltage, it

55 is obvious that these two points coincide electrically and thus closethe delta. The equivalent circuit of Fig. 3 is shown in Fig. 4. Thevalue of resistance in each leg 104, 106, or 108 of the delta 102 is theparalleled sum of all filament to filament or conducting line toconducting line resistances representing that particular leg.

The pick-off 109 is used to measure the pick-off phase and voltage withrespect to ground 110, thus the A. C. voltage source or transformersecondary which feeds the potentiometer should be connected centergrounded Y.

In Fig. 5, there is shown a vector diagram 112 for the potentiometer andpick-01f voltages and their respective phase angles. As mentioned above,the variation of or phase angle is essentially linear with variation of13 or mechanical angular motion of the pick-off, at least over smallareas of the potentiometer.

Theoretically, this is not strictly possible with three phaseexcitation. From the vector diagram in Fig. 5, it can be shown that Itis of interest to examine the quantity fl, which is called the phaseerror, e, since its value will indicate any deviation from the desiredlinearity. The phase error is thus:

V35, -1 H E 6 tan 2400 5 q This function repeats every 120 in [3. Fig. 6shows graphical representations 114 and 116 of e versus p3, as given inEquation 2 above for three (3) phase and four (4) phase excitations. Itwill be noted that an error in electrical phase up to 111 will exist forcertain values of ,8. (As an average value for the potentiometer, anerror of 11 in electrical phase corresponds to about A; in mechanicalangle ,8).

The curve 120 in Fig. 7, showing 5 versus ,8, was plotted fromexperimental data taken from a typical segment of the potentiometer. Thedeviation from linearity which is apparent from the curve 120 is in goodagreement, at least within the limits of accuracy inherent in themeasuring technique employed, with the theoretical deviation which couldbe expected.

From the same vector diagram 112 of Fig. 5, it is possible to show thatthe amplitude of the pick-off voltage with respect to ground 110 isgiven by the relation max E *2 sin 150 (3) a function which repeatsevery 120 in b. Curve 124 of E vs. is shown plotted in Fig. 8 for anarbitrarily selected value of Emax. Actual pick-off voltage as afunction of phase shift for two typical segments of the potentiometer isshown by curves 126 and 128 of Figs. 9 and 10.

It is well to point out that four phase excitation reduces thetheoretical maximum phase errors by a factor of nearly three and alsoreduces the magnitude of the voltage amplitude fluctuations. Thetheoretical phase error that might be expected with four phaseexcitation is shown by curve 116 of Fig. 6 for comparison with threephase excitation.

As mentioned previously, it is desirable to introduce certaincompensation factors into the 5, [3 relationship.

Referring now to section 12, Fig. 1, the potentiometer was so designedthat This relation describes the interferometer lobe pattern in space,where )t is the radiation wave length and d the antenna horn spacing. Byvarying the pick-off radius, it is possible to change the A/ d ratiothrough certain limits. Fig. 11, showing a curve 132 of 6 versus iqfi/360, was plotted from experimental data and agrees closely with Equation4.

Sections 14 and 16 of the potentiometer were designed to produce anearly linear {3 relationship, and still provide for Md alterationthrough a variable pick-off radius arm. Experimental results plotted forsection 16, Fig. 12, show a curve 138 such that the relation is linearout to the region 5::30. Almost similar results could be expected fromsection 14 of the potentiometer as previously described.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

What is claimed is:

1. A continuously adjustable polyphase voltage divider resistor,comprising, a base having at least two faces, a plurality of sets ofconductive elements located on the first of said two faces, theconductive elements of respective sets being arranged in regularrecurrent sequence with respect to each other, each set includingelements connected electrically to each other, resistance materialdistributed over the first face of said disk and in contact with saidconductive elements, a plurality of slip rings corresponding in numberto said plurality of sets of conductive elements, said slip rings beinglocated on the second face of said two faces, means for connecting eachset of conductive elements to a separate slip ring, and contact meansbearing on said resistance material, said contact means being arrangedto be shifted toward and away from the center of said base.

2. A continuously adjustable polyphase voltage divider resistor,comprising a base having at least two faces, a plurality of sets ofconductive elements located on the first of said two faces, theconductive elements of respective sets being arranged in regularrecurrent sequence with respect to each other, said conductive elementsin each set being substantially parallel and evenly spaced, each setincluding elements connected electrically to each other, resistancematerial distributed over said first face of said disk and in contactwith said conductive elements, a plurality of slip rings correspondingin number to said plurality of sets of conductive elements, said sliprings being located on the second face of said two faces, and means forconnecting each set of conductive elements to a separate slip ring.

3. A continuously adjustable polyphase voltage divider resistor,comprising, a base having at least two faces, a plurality of sets ofconductive elements located on the first of said two faces, theconductive elements of respective sets being arranged in regularrecurrent sequence with respect to each other, with the conductiveelements in each set being angularly arranged and substantially evenlyspaced with respect to each other so as to converge to a common center,each set having elements connected electrically to each other,resistance material distributed over said second face of said two facesof said disk in contact with said conductive elements, a plurality ofslip rings corresponding in number to said plurality of sets ofconductive elements, said slip rings being located on the second face ofsaid two faces, means for connecting each set of conductive elements toa separate slip ring, and contact means bearing on said resistancematerial, said contact means being arranged to B= isin- Eq. 4

be shifted toward and away from the center of said base.

4. An arrangement as set forth in claim 3, wherein the conductiveelements of each set converge to a center other than the center of saidbase.

5. An arrangement as set forth in claim 3, wherein said contacts can bemoved in a curved path in addition to being shifted toward or away fromthe center of the base of said resistor.

References Cited in the file of this patent UNITED STATES PATENTS GarmanJan. 21, 1941 Faus July 8, 1941 FOREIGN PATENTS France Mar. 30, 1943France May 7, 1942

